The present invention relates to apparatus and methods for effecting ultrasonic bonding on at least one continuously moving web or work piece. The invention more particularly concerns apparatus and methods for ultrasonically bonding at least one continuously moving web using a rotary anvil roll in combination with a rotary ultrasonic horn.
It is known to bond at least one continuously moving substrate web by constrictively passing the web through a nip defined between a rotating ultrasonic horn and a rotating anvil roll. Typically, the anvil roll includes one or more arrays of raised projections configured to bond the web in a predetermined bond pattern. The rotary ultrasonic horn is capable of expressing ultrasonic energy at a bonding surface so as to ultrasonically bond the web as the web travels through the nip.
The consistency and quality of the bond when using such rotary bonding techniques is dependent on, among other parameters, the consistency of the force exerted on the web by the combination of the anvil roll and the ultrasonic horn; the time during which the web is under compression in the nip; the size, shape, depth, and percent bond area of a bond pattern, where the area of the bond projections as a percentage of the total surface area of the bonded region defines the percent bond area; and the properties of material or materials being bonded. The consistency and quality of the bonds are also dependent on the frequency and amplitude of the vibrations of the ultrasonic horn.
Consistency and quality of bonds when using conventional rotary ultrasonic bonding methods and apparatus has been particularly variable where the desired bond pattern is intermittent, especially where the force expressed at the nip changes significantly, and may drop to substantially zero, in concert with the intermittent nature of the intermittency of the bonding operation.
When using conventional methods for rotary bonding in such configuration, the bond quality has typically been less than satisfactory along the length of the bond pattern. According to the invention, such inconsistency in the bond pattern has been due, at least in part, to inconsistent levels of force being effectively applied along the lengths of the respective intermittent bond regions of the bond pattern. Typical of such inconsistency is relatively greater nip loading at the leading edge of the bond region, and relatively lesser nip loading behind the leading edge of the respective element as the bonding apparatus flexes or deflects in combination with the passing of the respective bonding region, typically a raised bonding element, through the nip. Both the relatively greater nip loading and the relatively lesser nip loading comprise undesired inefficiency of control of nip pressure at the respective loci, and can result in poor bond quality and poor bond consistency.
Under excessive loading, which may be encountered at the relatively greater loading levels, so much energy may be applied to the materials being bonded as to burn through or otherwise excessively soften the materials being bonded, as well as to apply excessive pressure to the softened materials, whereby bonds so formed may be weak, and/or the bonds after cooling may be uncomfortably harsh to the touch of a wearer""s skin. In the alternative, excessive loading can physically damage, as by tearing, the material being bonded. Additionally, excessive loading can result in increased rates of wear on the ultrasonic horn and/or anvil roll, or can damage the horn and/or anvil. Finally, ultrasonic horns are generally driven by piezoelectric crystals that convert electrical energy at high frequency into mechanical vibrations. When an excessive impulse load is applied to the horn, the mechanical process works in reverse to cause a resulting electrical spike which can overload and shut down the electrical frequency generator.
Generating ultrasonic bonds depends on the combination of frequency and amplitude of the vibrations, the amount of pressure applied at the nip, and the time during which pressure is applied. Under conditions of insufficient loading at the nip, too little pressure is applied to the materials to be softened thereby, whereby the amount of energy transferred to the elements to be bonded together is insufficient to develop sufficiently strong bonds.
The above-mentioned difficulties of maintaining desired bond quality and consistency along both the length and width of the web become even more acute when intermittently bonding at least one continuously moving web using a rotary ultrasonic horn. Operation of a rotary ultrasonic horn includes movement inherent in the continuous vibration of the horn at a given frequency and amplitude to efficiently bond the web, as well as rotation of the horn as the web passes between the horn and the anvil at the nip. The web may vary in thickness along the length of the web, thus to impose varying resistance to the nip pressure being applied by the combination of the horn and the anvil on the web. Under certain conditions, such vibratory motion of the horn, and variation of web thickness, either alone or in combination, may adversely affect bond consistency and quality in the web if suitable steps are not taken to account for such thickness variation.
In addition, where the web advancing through the nip, defined between the horn and the anvil, varies in thickness and/or density, the web may apply a correspondingly varying back pressure on the horn and anvil. Thus, the overall result of variation in nip pressure, can be defined in terms of, among other parameters, the combination of the degree of variability in manufacturing and mounting the horn and anvil, as well as the degree of variability in thickness of the web moving through the nip between the anvil and horn.
These difficulties are even further exacerbated when the rotary ultrasonic bonding includes an intermittent bond pattern as discussed above such that a discrete raised array of bonding projections is introduced into the nip at the initiation of bonding of each bond region.
It is an object of this invention to provide bonding apparatus and methods wherein nip pressure is more uniform along the lengths and widths of respective bonding regions.
It is a further object to provide a transition gradient on a respective anvil roll being shaped to facilitate vertical acceleration and vertical deceleration of a complimentary ultrasonic horn.
It is yet a further object to provide a loading surface on an anvil roll, which is shaped to preclude effective bonding interference between the anvil roll and a cooperating rotary ultrasonic horn.
In a first family of embodiments, the invention comprehends a ramped anvil roll for cooperating with an ultrasonic horn and thereby creating ultrasonic bonds in a work piece passing between the anvil roll and a respective such ultrasonic horn. The ramped anvil roll has first and second sides of the anvil roll defining an anvil roll width therebetween, and the anvil roll further comprises a circumference thereabout. A relatively smaller radius portion of the anvil roll extends about a first portion of the circumference, and a relatively larger-radius raised bonding element extends about a second portion of the circumference. The raised bonding element has a front end portion, a rear end portion, a width defined by first and second sides thereof, and a raised operating surface defined between the first and second sides of the raised bonding element, and between the front end portion and the rear end portion. An outer surface at at least one of the front end portion and the rear end portion of the raised bonding element defines a transition gradient between the raised operating surface and the relatively smaller radius portion of the anvil roll. The transition gradient defines a modified sinusoidally-shaped curved loading surface including an inflection locus, the curved loading surface representing a relatively constantly changing angle as measured against respective radii of the anvil roll in combination with advancing along the corresponding portion of the circumference of the anvil roll.
The transition gradient can correspond with about 0.40 inch to about 0.60 inch of the circumference of the anvil, and preferably about 0.30 inch to about 0.70 inch of the circumference of the anvil.
The anvil roll can have a width of about 0.60 inch to about 6.00 inches, preferably about 1.25 inches to about 6.00 inches. Regardless of the desired width of a respective anvil roll, the width of a resultant bond pattern created using the anvil roll is less than or substantially equal to the width of the anvil roll.
One or both of the loading surface and the raised operating surface of the raised portion of the anvil roll can comprise an array of projections thereon spaced from each other and extending along the respective second portion of the circumference of the anvil roll, and across the entirety of the transverse width of the at least one raised portion, thereby covering substantially the respective entirety of one or both of the loading surface and the operating surface of the raised portion of the anvil roll.
Alternatively, one or both of the loading surface and the raised operating surface of the raised portion of the anvil roll can comprise an array of projections thereon, the projections being disposed in discrete spaced arrays which cover portions but not all of either or both of the respective circumference or width attributes of either or both of the loading surface and the operating surface of the raised portion of the anvil roll.
A pattern of projections about the loading surface and/or the raised operating surface of the raised portion of the anvil roll can generally define a resultant bond pattern wherein the resultant bond pattern represents about 20 percent to about 40 percent bond area and, correspondingly, about 80 percent to about 60 percent non-bond area.
In preferred embodiments, a resultant bond pattern from a first pattern of projections distributed about a portion or the entirety of the loading surface of the anvil roll represents the same or less percentage bonded area as a second pattern of projections distributed about a portion or the entirety of the raised operating surface of the anvil roll.
The second radius can be about 0.002 inch to about 0.07 inch greater than the first radius, and preferably about 0.01 inch to about 0.05 inch greater than the first radius.
In preferred embodiments, the loading surface of a given transition gradient is shaped to facilitate both vertical acceleration and vertical deceleration, of such ultrasonic horn as the horn moves from the smaller radius portion to the raised operating surface, or from the raised operating surface to the smaller radius portion.
The transition gradient can be disposed at the front end portion of the raised bonding element of the anvil roll; optionally at both the front end portion and the rear end portion of the raised bonding element.
The loading surface of the transition gradient can generally comprise a leading edge and a trailing edge. The leading edge of the transition gradient is typically defined at a radius at least as great as the first radius and less than the second radius. The trailing edge of the transition gradient is typically defined at the second radius and corresponds with the leading edge of the raised operating surface. The inflection locus is generally defined between the leading and trailing edges. The loading surface can be shaped to preclude effective bonding interference between the rotary anvil roll and a cooperating rotary ultrasonic horn, for bonding an absorbent article substrate, between the inflection locus and the leading edge of the raised operating surface.
In some embodiments, the trailing edge is generally defined at a radius at least as great as the first radius and less than the second radius, the leading edge being defined at the second radius and corresponding with the trailing edge of the loading surface, the inflection locus being disposed between the leading and trailing edges of the loading surface, the loading surface being shaped to preclude effective bonding interference between the rotary anvil roll and a cooperating rotary ultrasonic horn, for bonding an absorbent article substrate, between the inflection locus and the trailing edge of the raised operating surface.
In a second family of embodiments, the invention comprehends ultrasonic bonding apparatus for intermittently creating ultrasonic bonds in sequentially advancing absorbent article work piece segments, in a nip, wherein the work piece segments are up to about 0.25 inch thick at respective bonding loci. The ultrasonic bonding apparatus comprises a ramped anvil roll mounted for rotation about a first axis, and a rotary ultrasonic horn mounted for rotation about a second axis, generally aligned with the first axis. First and second sides of the anvil roll define an anvil roll width therebetween, the anvil roll further comprising a circumference thereabout. A relatively smaller radius portion of the anvil roll extends about a first portion of the circumference, and a relatively larger-radius raised bonding element extends about a second portion of the circumference. The raised bonding element has a front end portion, a rear end portion, a width defined by first and second sides thereof, and a raised operating surface defined between the first and second sides of the raised bonding element, and between the front end portion and the rear end portion. An outer surface at at least one of the front end portion and the rear end portion of the raised bonding element defines a transition gradient between the raised operating surface and the relatively smaller radius portion of the anvil roll. The transition gradient defines a modified sinusoidally-shaped curved loading surface including an inflection locus, the curved loading surface representing a relatively constantly changing angle as measured against respective radii of the anvil roll in combination with advancing along the corresponding portion of the circumference of the anvil roll. The horn comprises a radius, a circumference, a width, and a bonding surface. The ultrasonic horn and the anvil roll, in combination, are mounted and configured such that the ultrasonic horn and the anvil roll can be brought together to define a nip therebetween, wherein the anvil roll and the ultrasonic horn can rotate in common with movement of absorbent article work piece elements passing through the nip, and corresponding intermittent passage of the raised bonding element through the nip, accompanied by intermittent bonding of such work piece elements. The horn and the anvil roll define sufficient nip pressure to develop ultrasonic bonds in absorbent article substrate material of the work piece segments passing through the nip.
The anvil roll and the horn can be mounted and configured such that, when the raised portion of the anvil roll passes into and through the nip, the presence of the raised portion in the nip, in combination with any interference between the raised portion of the anvil roll and the horn, imposes stress on both the horn and the anvil roll, thus providing suitable force at the nip to develop ultrasonic bonds in absorbent article substrate material passing through the nip, using ultrasonic energy being expressed by the horn.
The anvil roll and the horn can be mounted and configured such that, when the raised portion of the anvil roll is not disposed in the nip, the smaller radius portion of the anvil roll is disposed in the nip, and the nip force is substantially less than a force required to form ultrasonic bonds at the nip.
In some embodiments, the anvil roll and the horn can be mounted and configured such that, when the raised portion of the anvil roll is not disposed in the nip, the smaller radius portion of the anvil roll is disposed in the nip, and the nip force is at least a minimum force required to form ultrasonic bonds at the nip, in suitable absorbent article work pieces.
In a third family of embodiments, the invention comprehends a ramped anvil roll for cooperating with an ultrasonic horn and thereby creating ultrasonic bonds in a work piece passing between the anvil roll and a respective such ultrasonic horn. First and second sides of the anvil roll define an anvil roll width therebetween, the anvil roll further comprising a circumference thereabout. A relatively smaller radius portion of the anvil roll extends about a first portion of the circumference, and a relatively larger-radius raised bonding element extends about a second portion of the circumference. The raised bonding element has a front end portion, a rear end portion, a width defined by first and second sides thereof, and a raised operating surface defined between the first and second sides of the raised bonding element, and between the front end portion and the rear end portion. An outer surface at at least one of the front end portion and the rear end portion of the raised bonding element defines a transition gradient between the raised operating surface and the relatively smaller radius portion of the anvil roll. The transition gradient defines a modified sinusoidally-shaped curved loading surface including an inflection locus, the curved loading surface being configured such that vertical velocity of such ultrasonic horn at a portion of the transition gradient juxtaposed adjacent the raised operating surface is substantially zero under conditions wherein target nip pressure between the anvil roll and such rotary ultrasonic horn at the raised operating surface is effective to develop ultrasonic bonds in an absorbent article substrate.
The ramped ultrasonic anvil roll can further comprise a surface defined between the first and second sides of the anvil roll, and around the relatively smaller radius portion of the anvil roll, wherein at least a portion of the surface of the anvil roll comprises an array of bonding projections thereon spaced from each other and extending along at least a portion of the relatively smaller radius portion of the circumference of the anvil roll, and across at least a portion of the transverse width of the anvil roll.
In a fourth family of embodiments, the invention comprehends a method of creating ultrasonic bonds in sequentially advancing absorbent article substrate work piece segments, wherein the work piece segments to be bonded are up to about 0.25 inch thick. The method comprises passing the work piece segments through a nip defined by an ultrasonic horn, and an anvil roll mounted for rotation about a first axis, the anvil roll comprising a width and a circumference. The anvil roll further comprises a first relatively smaller radius portion extending about a first portion of a circumference of the anvil roll and at least one raised bonding element having a second relatively larger radius extending about a second portion of the circumference of the anvil roll, and a rotary ultrasonic horn mounted for rotation about a second axis, aligned with the first axis. The method also comprises bringing the ultrasonic horn and the anvil roll together in defining the nip with interference at the raised bonding element, and correspondingly developing suitable pressure in the nip to create ultrasonic bonds in the absorbent article work pieces. The method further comprises activating ultrasonic energy in the ultrasonic bonding horn. Additionally, the method includes rotating the ultrasonic horn and anvil roll in common with movement of the work piece segments through the nip, and thereby intermittently applying pressure to the work piece segments at the raised bonding element, and creating ultrasonic bonds in the work piece segments passing through the nip.
The raised bonding element further comprises an operating surface represented by an area defined by the width of the raised bonding element and the second portion of the circumference of the anvil roll.
The anvil roll preferably comprises a transition gradient between the first portion of the circumference of the anvil roll and the raised bonding element, the transition gradient comprising a modified sinusoidal curve including an inflection locus. The transition gradient generally defines a series of potentially continuously changing radii along a portion of the circumference of the anvil roll, product of the transition gradient and width of the raised bonding element defining a loading surface of the transition gradient.
The rotary ultrasonic horn comprises a radius, a circumference, a width, and a bonding surface,
The loading surface and the operating surface of the raised bonding element of the anvil roll optionally can comprise an array of bonding projections thereon, the projections being disposed in discrete spaced arrays which cover all of the circumference and width, or portions but not all of either or both of the circumference or width, of the loading surface and the operating surface of the raised bonding element of the anvil roll.
A pattern of bonding projections about the loading surface and operating surface of the raised bonding element of the anvil roll generally controls a longitudinal arrangement of a resultant bond pattern.
In some embodiments, the raised bonding element of the anvil roll, including a first larger radius portion of the anvil roll, can provide bonding activity at thinner sections of a web of material, and the second relatively smaller radius portion of the anvil roll can provide clearance between the anvil roll and the horn for passage of relatively thicker sections of the web between the anvil roll and the horn.
In some embodiments, when the raised bonding element of the anvil roll passes into and through the nip, the presence of the raised bonding element in combination with interference between the raised bonding element of the anvil roll, and the horn, imposes stress on both the horn and the anvil roll, thus providing suitable force at the nip to develop ultrasonic bonds using ultrasonic energy being expressed by the horn.
In some embodiments, when the raised bonding element of the anvil roll is not disposed in the nip, and the smaller radius portion of the anvil roll is disposed in the nip, the nip force is substantially less than the force required to form ultrasonic bonds.